motor control and disease

Question 1

what is the role of lower and upper motor neurons?

Answer 1

lower motor neurons initiate movement of skeletal muscles
upper motor neurons regulate activation of lower motor neurons

Question 2

what happens when you stimulate the primary motor cortex on one side of the brain and why?

Answer 2

contralateral muscles contract (muscles on the opposite side of the body)
because axons in the corticospinal tract project contralaterally

Question 3

what is the role of the primary motor cortex and brainstem in movement?

Answer 3

the primary motor cortex is involved in planning, initiating and directing voluntary movements
the brainstem controls basic movements and posture

Question 4

how is the primary motor cortex mapped?

Answer 4

the lower body is mapped medially
the upper body is mapped laterally
proportions of the areas of the brain reflex the density of innervation in the muscles

Question 5

what is the corticospinal tract and what is it used for?

Answer 5

the pathway that upper motor neuron axons in the primary motor cortex follow to lower body neurons
it is used for voluntary limb movements

Question 6

what is the ventromedial pathway and what is it used for?

Answer 6

the pathway that axons from upper motor neurons in the brainstem follow to lower motor neurons
it is used for balance and posture
it is ipsilateral so if stimulated on one side muscles on the same side will be activated

Question 7

what are the 3 ventromedial pathways and what do they do?

Answer 7

the vestibulospinal tract: regulates head balance and posture
the tectospinal tract: keeps eyes straight as we move
the reticulospinal tract: keeps our body upright

Question 8

where are lower motor neurons located?

Answer 8

in the ventral horn of the spinal cord

Question 9

what are the 3 types of muscles and what movements do they control?

Answer 9

axial muscles control trunk movement
proximal muscles control movement of shoulders, elbows, knees and pelvis
distal muscles control movement of hands, feet and digits

Question 10

what is a motor unit and what is a motor pool?

Answer 10

a motor unit is a motor neuron and all the muscle fibres it innervates
a motor pool is all the motor neurons that innervate a single muscle

Question 11

how are motor pools organised?

Answer 11

they are spatially arranged in the spinal cord and extend over several segments of the vertebrae
different motor pools can overlap but they each have a specific position in the ventral horn
they are somatotopically arranged so are in the same order as the muscles they innervate

Question 12

how is movement anticipated?

Answer 12

it starts in the premotor areas and activates indirect projection to axial muscles by the reticular formation

Question 13

how is movement initiated?

Answer 13

it starts in the primary motor cortex and activates direct projection to the spinal cord by the corticospinal tract

Question 14

why do calf muscles contract first if we lift something up?

Answer 14

anticipation of movement is activated first

Question 15

what is motor neuron disease and what causes it?

Answer 15

a degenerative disease of motor neurons
it is caused by muscle atrophy and sclerosis in the spinal cord causing axons in the corticospinal tract to degenerate

Question 16

what does lower motor neuron disease cause?

Answer 16

it causes muscle weakness and paralysis
loss of muscle tone caused by loss of stretch reflexes
severe muscle atrophy
death due to lung dysfunction

Question 17

what does upper motor neuron disease cause?

Answer 17

muscle weakness
spasticity due to increased muscle tone from over-active stretch reflexes
loss of fine movement
death from loss of input to throat and tongue muscles

Question 18

how does excitotoxicity cause motor neuron disease and how can it be treated?

Answer 18

neurons are overstimulated by glutamate causing them to die
can be treated using drugs that block glutamate release

Question 19

what is the basal ganglia, what does it contain and how is it regulated?

Answer 19

it is a structure in the forebrain involved in initiating movement
it contains the caudate, putamen and globus pallidus
it is regulated by the substantia nigra

Question 20

what is the motor loop?

Answer 20

the motor cortex is connected to the basal ganglia which feeds back to the premotor cortex via the ventrolateral complex (VLo) in the thalamus

Question 21

what are the 2 pathways of the motor loop?

Answer 21

direct where the VLo is inhibited
indirect where the VLo is activated

Question 22

what is parkinsons disease?

Answer 22

a neurodegenerative disease that is mostly random but can be genetic

Question 23

what are the symptoms of parkinsons?

Answer 23

hypokinesia (loss of movements)
bradykinesia (slower movements)
akinesia (no movement)
increased muscle tone

Question 24

what causes parkinsons disease?

Answer 24

loss of dopaminergic neurons
degeneration of the substantia nigra
neurons contains Lewy bodies

Question 25

how can parkinsons be treated?

Answer 25

a dopamine precursor called L-dopa

Question 26

what is huntingtons disease?

Answer 26

a rare neurodegenerative disease that is mostly hereditary and progresses over time

Question 27

what are the symptoms of early and late huntingtons disease?

Answer 27

early: hyperkinesia (increased movement) and chorea (involuntary jerking) late: akinesia and dystonia (muscle spasms)

Question 28

what causes huntingtons disease?

Answer 28

an autosomal dominant gene it degenerates neurons in the striatum

Question 29

what causes predisposition to parkinsons?

Answer 29

mutations in multiple genes some are rare but have high penetrance and others are more common but have low penetrance

Question 30

what causes a predisposition to huntingtons disease?

Answer 30

a mutation in a specific gene that encodes for huntingtin protein

Question 31

what is the role of parkinsons genes?

Answer 31

they encode for proteins involved in protein degredation pathways that produce Lewy bodies

Question 32

what is the role of the cerebellum in motor control?

Answer 32

it is required for learning and execution of planned and voluntary movement involved in multijoint movement

Question 33

how does the cerebellum allow motor learning?

Answer 33

it instructs the motor cortex to control the direction, timing and force of movement based on predictions of the movement output

Question 34

how does the cerebellum predict movement output?

Answer 34

based on past experiences of the movement it receives sensory input from around the body and projects it back to the motor cortex